Phased array antennas are normally composed of a number of individual radiating elements coupled to an input by virtue of a number of phase shifters operative for ensuring that signals radiated from the radiating elements are "in phase" or otherwise coherently added together. Each phase shifter normally corresponds to a specific radiating element and is operative for shifting the phase of signals so that all signals received from a particular direction will be in step with one another. Similarly, all signals radiated by the individual elements of the antenna will be in step with one another in some specific direction.
Changing the phase shift at each element alters the direction of the antenna beam. An antenna of this kind is called an electronically steered phased-array. Electronically steered phased arrays allow rapid changes in the position of the beam without moving large mechanical structures. In some systems, the beam can be changed from one direction to another within microseconds.
In future communication systems including satellites having phased array antennas, a large number of narrow antenna beams may provide a wide variety of communications services to ground terminals around the world. For low-earth-orbit (LEO) satellites, these beams must be continually steered in angle to maintain coverage of the earth terminals as the satellites move through their orbits. For geosynchronous-equatorial-orbit (GEO) communication satellites, there may be the need to reposition the communication beams as market conditions and regions change. However, while the foregoing principles are well known, there is no known practical phased array antenna topology operative at millimeter wave frequencies. Furthermore, there is no known phased array topology practical at millimeter wave frequencies for forming simultaneous multiple beams from a single aperture which can be independently steered over a wide angle field of view.
Accordingly, a need exists for the formation of simultaneous independently steerable multiple beams in a phased array antenna that is practical at millimeter wave frequencies.